Method for purifying liquids

ABSTRACT

A method for purification of drinking water and other liquids includes providing a generally cylindrically-shaped open-ended tube for flow of the liquid therethrough, the tube comprising a transducer for converting electrical energy to acoustic energy, providing a liquid moving means for flowing the liquid through the tube, and providing an electrical power source for providing electrical power to the tube. The method further includes operating the liquid moving means to flow the liquid through the tube, and operating the power source to transmit ultrasound through the liquid in the tube to induce cavitation in the liquid in the tube. The cavitation inactivates microorganisms in the liquid.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 10/383,197, filed Mar. 6, 2003, in the name of Robert F. Carlson et al.

This application further claims the benefit of U.S. Provisional Patent Application Ser. No. 60/364,014, filed Mar. 13, 2002, in the name of Robert F. Carlson et al.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the purification of drinking liquids and is directed more particularly to a method for effecting the purification.

2. Description of the Prior Art

Attention has been focused on enhancing the safety of drinking water. Federal standards for bacteriological quality in drinking water have evolved steadily since the beginning of the last century, culminating in the Safe Water Drinking Act of 1974 and two significant amendments thereto, in 1986 and 1996. Over the years, domestic public water systems have improved the standards under which they operate, and water at the point of entry (POE) of distribution has generally been considered safe.

However, in recent years the public attitude toward the quality of the water supply at the POE has shifted. According to a 1999 survey by the Water Quality Association, one in five households was dissatisfied with the quality of their water supply. Better methods of pathogen detection, failing infrastructures in some communities, and concerns about the chemicals used in the treatment of water, are a few of the reasons. Drinking water quality is a special concern for Americans living in rural areas, where some waterborne pathogens are commonly found. Research has shown an abundance of Cryptosporidium and Giardia on dairy farms, both in the U.S. and abroad. Many rural communities do not have a large public water system and are vulnerable to waterborne pathogens.

Therefore, it is important to ensure the safety of drinking water from micro-organisms at the individual household levels, or POU. Events of Sep. 11, 2001, and the consequent “war on terrorism”, have further caused the shift in public thinking relative to the safety of Americans, both at home and abroad.

From the ground or surface water, delivery of drinking water to the consumer takes three main routes. First, municipalities undertake the task of purifying the water and supplying it to the consumers. Secondly, consumers use their own wells or other techniques for obtaining water. Lastly, commercial bottled water companies produce pure drinking water using either water from municipalities or water from other direct sources.

As a result of increased pathogen detection, and bio-terrosim threats, along with a general lack of funding for upgrading municipal water supplies, consumers are increasingly exploring the safe drinking water options. According to the 2001 Water Quality Association national survey, the percentage of U.S. population with home water treatment devices has increased from 27% in 1995 to 41% in 2001. It is estimated that more than ten million households will be looking for further enhancements of pathogen removal in their drinking water. The key providers in this market are water filtration companies using reverse osmosis or other nano-filtration technologies. However, there are many commercial water purification products in the market. Typically, they employ a combination of chemical, ultra violet radiation, ozonation, and filtration treatments in order to achieve maximum effectiveness, inasmuch as one method alone does not ensure protection against all micro-organisms.

Waterborne organisms of concern can be classified by their size (Table 1). TABLE 1 Relative Size of Waterborne Micro-Organisms Approximate size Micro-organisms (in microns) Examples Viruses 0.002-0.5  Hepatitis, 0027 micron Meningitis, .2 micron Bacteria, cocci 0.5-1.5 Pseudomonas, (spherical) and 0.5-0.62 micron bacilli (rod-shaped) Vibrio cholerae, 1 micron Protozoa  2-15 Giardia lamblia, 9-12 micron Cryptosporidium, 4-6 micron

purification in use today employ a combination of techniques classified in five main categories. Their application areas, principles of operation, effects on surviving microorganisms, and limitations of the processes are shown in Table 2. TABLE 2 Summary of Different Water Treatment Processes Treatment Done at Operating Principle Effect on survivors Limitations Ultraviolet POU mutagen Interference with Limited impact on hard- DNA replication shelled micro-organisms Chlorination POE/ Production of Evolution of resistant chlorination by-products, POU Hypochlorous acid bacterial cells from not effective against C. that kills microbial the fittest survivors parvum pathogens Thermal POU denaturation of lethal above certain Requires high input of proteins temperature (usually energy to raise the 65°) temperature to sufficient level Filtration POU Separates the None Flow rates, maintenance microbes from the water based on their sizes Ozonation POU/ oxidation of cell walls, oxidation Complex generation POE damage to nucleic process, Need to eliminate acid residual gases that may be toxic

It is clear that while all the techniques are effective to a certain extent, they have limitations in terms of operations, resistance of certain pathogens, and creation of toxic by-products. It is desirable to have a device that is effective against all kinds of microorganisms and will not generate toxic by-products.

Acoustic “cavitation” fills this need and is an ideal supplement to existing processes. Recent work has confirmed this by demonstrating that cavitation is effective in destroying E. coli and L. pneumophila. Cavitation is the phenomenon of creation in implosion of microscopic bubbles in a fluid and is caused by rapid changes in the fluid pressure. The primary mechanism of inducing the rapid change in pressure is transmission of ultrasound in the fluid. The sound is created either by a piezoelectric or magnetostrictive transducer. Coupling a sound transducer to the fluid medium and driving the transducer with sufficient power creates an alternating pressure cycle that induces cavitation.

The parameters that affect cavitation are input energy transmitted in the medium, frequency of the sound, number of sound pulses, and the ambient pressure of the fluid. Typically, the higher the frequency, the greater is the cavitation threshold and the smaller the bubble size. There are three distinct stages associated with cavitation:

-   -   1. Nucleation—Cavitation bubbles are formed.     -   2. Bubble growth—The bubbles grow by absorbing energy from the         alternating compression and expansion caused by ultrasound.     -   3. Implosion—The growing bubble reaches a critical size and         implodes upon itself, because it cannot absorb any more energy.

In the implosion stage, very high local temperatures and shearing forces are produced. The shear forces and high temperatures are utilized in a number of applications designed for cleaning (acoustic cleaners) and homogenizing tissue samples (sonicators).

There is a need for a water cavitation assembly which is relatively simple and of inexpensive construction, easy to operate, and which can easily be installed in drinking water systems at points of use.

SUMMARY OF THE INVENTION

An object of the invention is, therefore, to provide a method for purifying drinking water and other drinking liquids by acoustic cavitation thereof by use of a robust cavitation assembly at the POU.

With the above and other objects in view, a feature of the present invention is the provision of a method for purifying drinking liquids, particularly water, the method comprising the steps of providing a generally cylindrically-shaped open-ended tubular housing for flow of water or other liquid therethrough, an annular fiberglass layer disposed coaxially in the housing and spaced from the housing, a cylindrically-shaped non-toxic open-ended tube disposed coaxially in the fiber glass layer and spaced from the fiberglass layer, and defining an internal passageway for the flow of the liquid flowing the drinking liquid through the tube comprising a transducer for converting electrical energy to acoustic energy, and providing electrical power to the transducer to generate ultrasound and transmit the ultrasound through the liquid in the tube to induce cavitation in the liquid in the tube, wherein the cavitation operates to inactivate microorganisms in the liquid.

In accordance with a still further feature of the invention, there is provided a method for purifying drinking water or other liquid, comprising the steps of flowing the drinking liquid through a generally cylindrically-shaped open-ended non-toxic tube having ceramic rings mounted thereon, providing electrical power to the ceramic rings to generate ultrasound, and transmitting the ultrasound through the liquid in the tube to induce cavitation in the liquid in the tube, whereby to inactivate microorganisms in the liquid.

In accordance with a still further feature of the invention, there is provided a method for purifying drinking water or other liquid, comprising flowing the liquid through a generally cylindrically-shaped open-ended tubular housing having an annularly-shaped fiberglass layer disposed coaxially therein and spaced from the housing, and having ceramic rings disposed adjacent the fiberglass layer and disposed inwardly thereof, and providing electrical power to the ceramic rings to vibrate the rings to generate ultrasound, and transmitting the ultrasound through the liquid to induce cavitation in the liquid in the housing, wherein the cavitation in the liquid serves to inactivate microorganisms in the liquid.

The above and other features of the invention, including various novel details of construction and combinations of parts and method steps, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular assembly, apparatus, and method steps embodying the invention are shown by way of illustration only and not as limitations of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made to the accompanying drawings in which are shown illustrative embodiments of the invention, from which its novel features and advantages will be apparent.

In the drawings:

FIGS. 1A and 1B are diagrammatic flow charts illustrating use of the assembly and method singly and in groups;

FIG. 2 is a partly sectional view of a transducer portion of the assembly; and

FIG. 3 is a perspective view of a portion of the assembly of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For liquid purification, piezoelectric ceramic ring transducers are ideally suited for their ability to focus sound resulting in an efficient cavitation system. As shown in FIG. 1, they can be readily adapted to drinking water piping systems for individual household usage and can be scaled up by parallel connections for larger dwellings/buildings to meet the demands of the facility. Once an individual acoustic cavitation chamber is provided for an appropriate flow rate and is demonstrated to be effective, a multiplicity of like cavitation chambers can be combined to provide the necessary flow rate for bigger installations.

An illustrative drinking water acoustic cavitation assembly 20 includes a water moving means, such as a pump 22, for providing a suitable flow rate for a particular site. The assembly 20 further includes a generally cylindrically-shaped open-ended tubular housing 24 for flow of water therethrough. The housing 24 may be of metal, PVC, or a composite. It may be provided with threads 25, internal or external, or quick-connect and disconnect connectors for insertion and ready removal from a water pipe. An annularly-shaped fiberglass wrap 26 is disposed coaxially in the housing 24 and is spaced from the housing to form an annular chamber 28. O-rings 30 are disposed in the chamber 28 and abut the housing 24 and the fiberglass wrap 26 and serve to seal the chamber 28 against migration of water thereinto.

A cylindrically-shaped non-toxic open ended tube 32 is disposed coaxially in the fiberglass wrap 26 and is spaced inwardly therefrom. The non-toxic tube 32 preferably is of a metal or composite material. The non-toxic tube 32 and the fiberglass layer 26 define an annular space 34 in which are disposed ceramic rings 36. In manufacture, the fiberglass wrap 26 is applied to the outer surface of the ceramic rings 36, to pre-stress the ceramic rings, as is known in the art. The ceramic rings 36 are separated by isolation rings 38.

The assembly 20 includes a power source 40 which provides power through electrically conductive lines 42 to inside and outside surfaces 44, 46 (FIG. 3) of the ceramic rings 36. The surfaces 44, 46 are coated with silver plate and the wires 42 are soldered to the silver plate as at points 45. The ceramic rings are driven in parallel. Power is applied by way of an alternating voltage operating close to the natural frequency of the ceramic rings to achieve maximum vibration, and hence, maximum cavitation.

The ceramic rings 36 are selected to match a targeted frequency within a range of ultrasonic frequencies of about 30-200 kHz. Ideally, the cavitation field should be uniform within the tube 32 so that any micro-organism passing through the tube will experience the same dose of cavitation. However, the ceramic geometries and the superposition of different frequencies may alter the distribution. Since cavitation is associated with bubble formation and collapsing bubbles produce sound, places with higher bubble concentration will have a higher local sound level. The ceramic rings 36 may contain ceramics of different frequencies, wherein each ring vibrates at a different frequency.

The ends of the annular chamber 28 and the annular space 34 are closed by epoxy ribs 48.

A preferred embodiment of the assembly includes a 1.5 inch OD×2.0 inch long piezoelectric ceramic ring assembly encased within a PVC tubular housing with inlet and outlet connections 25 for hose attachments for water flow.

In use of the assembly 20, water proximate the POU is flowed through the cylindrically-shaped non-toxic tube 32 disposed within the ceramic rings 36 which, in turn, are wrapped with the fiberglass 26, all disposed within the generally cylindrically-shaped open-ended tubular housing 24. The water is flowed typically by a pump 22, but may be flowed by any means normally used in the system of concern, such as by gravity from a roof-top tank, or the like.

Such assemblies may be used as acoustic cavitation devices for inactivation of protozoa, bacteria and viruses. The cylinders can be plumbed to existing water pipes and activated only when water flow is detected. The advantages of such an acoustic cavitation purifier are two-fold: (1) it enhances the effectiveness of existing POU water treatments, and (2) it can be scaled up to serve the needs of a larger number of water consumers. The projected costs of such individual devices, less the water flow means and electrical power source, is quite low, less than U.S. $100 per point of use.

It will be apparent that many benefits can be derived from the invention. A principal advantage of this concept is its flexible nature. It can provide an additional level of security and robustness to already installed devices, or on its own it can be effective against a wide variety of pathogens, and reduce the need for chemical treatment of water and other drinking liquids. Potential application areas for small units are in the main water supply lines of single-family homes or on individual faucets. Scaled up bigger units can be used for enterprise level applications.

The advantages of “acoustic cavitation” over other types of liquid purification processes (as summarized in Table 2) include, working in conduction with the other processes, reduction of the need for chlorine or other chemical compounds, and breaching the shells of micro-organisms for better effectiveness of ultraviolet or ozonation treatments. Operating individually, the system offers advantages, such as simpler operation opposed to ozonation, robust operation of the ceramics, and elimination of the need for periodic change of filters.

There is thus provided a method for purifying drinking water at the POU, as well as other drinking liquids requiring purification.

It will be understood that many additional changes in the details, materials, method steps and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principles and scope of the invention as expressed in the appended claims. 

1. A method for purifying drinking liquids, the method comprising the steps of: flowing a drinking liquid through a generally cylindrically-shaped open-ended tube comprising a transducer for converting electrical energy to acoustic energy; and providing electrical power to the transducer to generate ultrasound and transmit the ultrasound through the liquid in the tube to induce cavitation in the liquid in the tube; wherein the cavitation so induced operates to inactivate microorganisms in the liquid.
 2. The method in accordance with claim 1 wherein said transducer is operated at ultrasonic frequencies of about 30-200 kHz.
 3. The method in accordance with claim 1 wherein the liquid is water and the tube is placed within an existing water line.
 4. The method in accordance with claim 3 wherein the tube is placed proximate a point of use.
 5. A method for purifying drinking liquids, the method comprising the steps of: flowing a drinking liquid through a generally cylindrically-shaped open-ended non-toxic tube having ceramic rings mounted thereon; and providing electrical power to the ceramic rings to generate ultrasound, and transmitting the ultrasound through the liquid in the tube to induce cavitation in the liquid in the tube; whereby to inactivate microorganisms in the liquid.
 6. The method in accordance with claim 5 wherein the liquid is water and the non-toxic tube is placed in a water supply conduit proximate a point of use of the water.
 7. A method for purifying drinking liquids, the method comprising the steps of: flowing a drinking liquid through a generally cylindrically-shaped open-ended tubular housing having an annularly-shaped fiberglass layer disposed coaxially therein and spaced from the housing, and having ceramic rings disposed adjacent the fiberglass layer and disposed inwardly thereof; and providing electrical power to the ceramic rings to vibrate the rings to generate ultrasound, and transmitting the ultrasound through the liquid to induce cavitation in the liquid in the housing; wherein the cavitation in the liquid serves to inactivate microorganisms in the liquid.
 8. A method for purifying drinking liquids, the method comprising the steps of: providing a cavitation assembly comprising: a generally cylindrically-shaped open-ended tube comprising a transducer for converting electrical energy to acoustic energy; a liquid moving means; and an electrical power source; operating the liquid moving means to flow the liquid through the tube; and operating the electrical power source to provide electrical power to the transducer to generate ultrasound and transmit the ultrasound through the liquid in the tube to induce cavitation in the liquid in the tube; wherein the cavitation inactivates microorganisms in the liquid.
 9. The method in accordance with claim 8 wherein the tube includes rings of ceramic material.
 10. The method in accordance with claim 9 wherein the tube and ceramic rings comprise a piezoelectric transducer.
 11. The method in accordance with claim 10 wherein the transducer is operated at ultrasonic frequencies of about 30-200 kHz.
 12. The method in accordance with claim 11 wherein the rings are of different ceramic materials and are operated at different ones of the frequencies.
 13. The method in accordance with claim 8 wherein the drinking liquid is water and the tube is placed within an existing water line.
 14. The method in accordance with claim 13 wherein the tube is placed proximate a point of use of the drinking water.
 15. The method in accordance with claim 5 wherein the liquid is water and the non-toxic tube is placed in a water supply conduit proximate a point of use of the water. 